Gas blast circuit breaker of the axial blast type with magnetic means for forcing the upstream arc terminal away from the center of the stagnation zone at the upstream electrode



T. H. LEE 3,330,927

1TH ING THE UPSTREAM ARC TERMINAL ER OF THE STAGNATION ZONE AT THE UPSTREAM ELECTRODE July 11, 19s? GAS BLAST CIRCUIT BREAKER OF THE AXIAL BLAST TYPE W MAGNETIC MEANS FOR FORC AWAY FROM THE CENT 2 Sheets sheet 1 Filed Aug. 16, 1963 uvvmvroa: THOMAS H. LEE, MM, 6"

ATTORNEY.

Juiy 11, 1967 T. H. LEE 3,330,927 GAS BLAST CIRCUIT BREAKER OF THE AXIAL BLAST TYPE WITH MAGNETIC MEANS FOR PORCING THE UPSTREAM ARC TERMINAL AWAY FROM THE CENTER OF THE STAGNATION ZONE AT THE UPSTREAM ELECTRODE Filed Aug. 16. 1963 2 Sheets-Sheet z OASTANCE FROM CENTER OFJTAG/VAT/O/V Z0/VE MAGNET/C FORCE INVENTOR. THo/vms H. LEE,

BY M I ATTORNEY.

United States Patent Office TION ZONE AT THE UPSTREAM ELECTRODE Thomas H. Lee, Nether Providence, Pa., assignor to General Electric Company, a corporation of New York Filed Aug. 16, 1963, Ser. No. 302,555 1 Claim. (Cl. 200-148) This invention relates to a gas blast circuit breaker of the axial blast type and, more particularly, to means for improving the interrupting ability of such a circuit breaker.

The usual gas blast circuit breaker comprises means for establishing an electric arc across a gap between two electrodesand mean for directing a high velocity blast of gas into the arcing region. The purpose of the gas blast is to cool the arc and to scavenge the arcing region of arcing products so as to increase the rate at which dielectric strength is built up across the gap when the current 'zero point is reached. By increasing this rate of dielectric recovery, it is possible to improve the ability of the gap to withstand the usual recovery voltage transient which builds up as soon as current zero is reached, thus improving the interrupting ability of the circuit breaker.

In an axial blast type of circuit breaker, there is typically provided an orifice through which the are between the electrodes extends and through which the gas blast flows axially of the are about the periphery of the arc. The purpose of the orifice is to guide the blast with respect to the arc and to impart the desired high velocity to the blast. The electrode that is located upstream from the orifice is referred to hereinafter as the upstream electrode and the electrode that is located downstream from the orifice is referred to hereinafter as the downstream electrode. In the typical axial blast circuit breaker, there is a stagnation zone on the downstream side of the upstream electrode. Typically, the gas blast forces the upstream terminal of the arc into the stagnation region and holds it captivetherein. I have found that, from an interrupting ability viewpoint, this is not an ideal position in which to maintain the upstream arc terminal. Both the scavenging process and the arc cooling process are relatively ineificient in the stagnation zone, because the air in this zone tends to move in large scale eddies of relative low velocity; and this low velocity detracts from b th scavenging and are cooling. An object of my invention is to improve the ability of the gas blast to effect arc-cooling and scavenging when the upstream arc terminal is located on the downstream side of the upstream electrode.

In carrying out my invention in one form, I provide an axial blast electric circuit breaker that comprises an 'upseream electrode and a downstream electrode between which an arc is established. Means is provided for causing a blast of pressurized gas to flow at high speed about the upstream electrode and axially of the arc. This axial blast envelops the upstream electrode and establishes a stagnation region on the downstream side of the upstream electrode. The upstream electrode is constructed in such a manner that the current path leading through the electrode to the upstream terminal of an arc in the stagnation zone extends radially outward. This results in a magnetic ,force on the are acting in a radially outward direction and having a magnitude varying as a direct function of the square of the current.

The distance that the arc terminal will be driven from the center of the stagnation region depends upon the magnitude of this radially outward acting magnetic force. The greater this magnetic force, the further the arc termi- 3,330,927 Patented July 11, 1967 nal will be driven radially outward from the center of the stagnation zone, but one until a certain critical location is reached, at which point the aerodynamic forces from the air blast strongly resist further radially outward movement. When the arc terminal reaches this critical location, large increases in magnetic force have no appreciable capacity to drive the arc terminal further radially outward. I shape the upstream electrode in such a manner that the radially outward acting magnetic force present when the instantaneous current exceeds 3,000 amperes is suificien-tly high to drive the arc terminal radially outward into this critical position.

For a better understanding of my invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross sectional view of a gas blast circuit interrupter embodying one form of my invention.

FIG. 2 is an enlarged sectional view of the upstream electrode of the circuit interrupter of FIG. 1.

FIG. 3 is an enlarged sectional view similar to FIG. 2 except showing an are on the electrode at various positions.

FIG. 4 is a graphical representation of certain force relationships present with the electrode of FIGS. 1-3.

FIG. 5 is a cross sectional view similar to FIG. 2 but showing a slightly modified form of the invention.

Referring now to FIG. 1, the circuit interrupter shown therein is of the sustained-pressure, gas-blast type described and claimed in US. Patent 2,783,338-Beatty, assigned to the assignee of the present invention. Only those parts of the interrupter that are considered necessary to provide an understanding of the present invention have been shown in FIG. 1. In this respect, only the right hand portion of the interrupter has been shown in section inasmuch as the interrupter is generally symmetrical with respect to a vertical plane and the left hand portion is substantially identical to the right hand portion. As described in detail in the above-mentioned Beatty patent, the interrupter comprises a casing 12 which is normally filled with pressurized gas to define an interrupting chamber 11. Located within the interrupting chamber 11 are a pair of relatively movable contacts 14 and 16 which can be separated to draw an are within the pressurized gas within the chamber 11. The contact 14 is relatively stationary, whereas the other contact 16 is mounted for pivotal motion about a fixed, current-carrying pivot 18. When the movable contact 16 is driven clockwise about the pivot 18 from its solid-line closed position of FIG. 1, an arc is established in the region Where the contacts part. The movable contact 16 is shown by dotted lines in FIG. 1 in a partially-open position through which it passes during a circuit-interrupting operation after having established an arc.

The movable contact 16 is supported by means of its current-carrying pivot 18 on a conductive bracket 19 that is preferably formed integral with a stationary cylinder 32. The cylinder 32 at its lower end is suitably supported from a generally cylindrical casting 33. The casting 33 at its lower end is suitably secured to a flange 35 rigidly carried by the stationary metallic casing 12.

For producing a gas blast to aid in extinguishing the arc, the cylindrical casting 33 contains a normally-closed exhaust passage 36 leading from the interrupting chamber 11 to the surrounding atmosphere. The casting 33 at its upper end is provided with a tubular nozzle-type electrode 38 having an orifice portion 39 at its outer end defining an inlet 37 to the exhaust passage 36. This inlet 37 is referred to hereinafter as the orifice opening. The flow of arc-extinguishing gas through the tubular nozzle 38 and the exhaust passage 36 is controlled by means of a cylindrically-shaped reciprocable blast valve member 40 located at the outer, or lower, end of the exhaust passage 36. This blast valve member 40 normally occupies a solidline, closed position wherein an annular flange 42 formed at its lower end sealingly abuts against a stationary valve seat 34 carried by the exhaust casting 33.

During a circuit interrupting operation, the movable blast valve member 40 is driven upwardly from its solidline,'closed position of FIG. 1 through a partially open intermediate position shown in dotted lines in FIG. 1. Opening of the valve member 40 allows pressurized gas in the chamber 11 to flow at high speed through the orifice opening 37 and nozzle 38 and out the exhaust passageway 36 past the valve member 40 to atmosphere, as indicated by the dotted line arrows B of FIG. 1. The manner in which the gas blast acts to extinguish the arc will soon be described in greater detail.

At its upper end, the cylindrical valve member 40 surrounds a projecting tubular support 41 upon which the valve member 40 is smoothly slidable. The tubular support 41 is fixed to the casting 33 by suitable means (not shown). A compression spring 44 positioned between the movable valve member 40 and the lower end of support 41 tends to hold the valve member 40 in its closed position against the valve seat 34.

To protect the support 41 and the upper end of the valve member 40 from the harmful effects of arcing, a protective metallic tube 43 is positioned about these parts and is suitably secured to the support 41. Secured to the outer surface of this tube is a downstream probe or electrode 45, preferably of a refractory metal, which projects radially from the tube 43 and transversely into the path of the gas blast flowing through the passageway 36. As will soon appear more clearly, the downstream terminal of the arc is transferred to this electrode 45 during an interrupting operation and, after such transfer, occupies a position generally corresponding to that shown at 46. The downstream electrode is preferably constructed as shown and claimed in Patent No. 2,897,324Schneider, assigned to the assignee of the present invention, so that it has a nonstreamlined upstream surface 48 that coacts with the gas blast to form a stagnation region upstream from the surface 48. The terminal of an are such as 46 reaching the electrode 45 is captured within the stagnation region and thus prevented from being driven further downstream by the gas blast.

For controlling the operation of the movable blast valve 40 and movable contact 16, a combined operating mechanism 50 is provided. This mechanism 50 is preferably constructed in the manner disclosed and claimed in the aforementioned Beatty Patent 2,783,338, and its details "form no part of the present invention. Generally speaking, this mechanism 50 comprises a valve-controlling piston 51 and a contact-controlling piston 52 mounted within the cylinder 32. The valve-controlling piston 51 is coupled to the movable valve member 40 through a piston rod 54 suitably clamped to the valve member 40. The contact-controlling piston 52, on the other hand, is connected to the movable contact 16 through a piston rod 58 and a cross head 59 secured to the piston rod. A link 60 pivotally joined to the cross head 59 at 61 and to the movable contact 16 at 62 interconnects the cross head 59 and the movable contact 16. When the valvecontrolling piston 51 is driven upwardly, it acts to open the valve member 40, and, simultaneously, to drive the contact-controlling piston 52 upwardly to produce opening movement of the movable contact member 16.

Opening movement of the contact member 16 first establishes an are between the ends of the contacts 14 and 16. Shortly thereafter, however, the blast of gas which has been flowing through the orifice opening 37,

as indicated by the dotted-line arrows B, forces the upstream terminal of the are on to an upstream arcing electrode 70, which is electrically connected to the stationary contact 14. As opening motion of the movable contact 16 continues, the gas blast forces the downstream terminal of the arc to transfer from the movable contact 16 to orifice structure 39*, which is electrically connected to the movable contact 16. The gas blast then impels the downstream terminal of the arc through the orifice opening 3-7 and nozzle 38 on to the upper end of the protective metallic tube 43. From there, the gas blast drives the downstream arc terminal downwardly and into the previously-described stagnation region adjacent the downstream surface 48 of the electrode 45. The are then occupies the position generally shown in 46. When the arc is in this position, the arc column extends through the orifice opening 37 and is subjected in the orifice region to an intense high velocity blast. This blast is effective to cool and deionize the arc and to prevent reignition thereof at an early current zero.

It is generally understood that the ability of the circuit breaker to prevent the are from reigniting at a current zero depends upon the rate at which dielectric strength is recovered across the arcing region when arcing ceases at current zero. The faster the dielectric recovery rate, the lower the chances for reignition and thus the better the chances for successful interruption at this point.

I have found that substantial improvements in this dielectric recovery rate can be made by magnetically forcing the upstream arc terminal radially outward from the center of the upstream electrode into a critical region at the edge of the stagnation zone present on the downstream side of the upstream electrode. This will now be explained in greater detail with particular reference being had to FIGS. 2-4. The stagnation zone can best be seen in FIG. 2, which is an enlarged cross sectional view of the upstream electrode showing the primary flow paths B adjacent the electrode that are followed by the air blast as it streams past the electrode. As shown in FIG. 2, these paths B follow the external contour of the electrode rather closely about the outer periphery of the electrode, but eventually separate from the surface of the electrode at points designated S in FIG. 2 near the outer periphery of the downstream face of the electrode. Similar points S are present about the entire downstream face of the upstream electrode at approximately the same distance from the central axis of the electrode as the depicted points S. Radially inwardly of these points S there is a zone 74 in which the air flows at a relatively low velocity in large scale eddies such as depicted in 75. This zone 74 I refer to as the stagnation zone.

The electrode 70 may be thought of as being of a cup-shaped configuration and as comprising a base portion 77 and an annular flange 78 projecting from the base portion in a direction opposite to the direction followed by the gas blast. Current enters the electrode 70 through current-directing means comprising a conductive supporting rod 79 which is spaced from the flange 78 about the entire periphery of the rod and is attached to the base 77 at a central region of the base '77.

The upstream terminal of any are established between the contacts 16 and 14 is transferred from the contact 14 on to the upstream electrode by the air blast following the path B. The air blast then drives the upstream terminal in the direction of the air blast into the stagnation zone 74. The aerodynamic forces exerted by the air blast on the arc tend to drive the upstream arc terminal into the center of the stagnation region. However, I prevent the upstream terminal from entering this central region by providing in the central region an insert 80 of are resistant insulating material. Preferably, this insulating material is polytetrafluoroethylene, which is sold under the trade name of Teflon. Since there is no exposed conductive surface in this central region for the upstream arc terminal to attach to, it is maintained radially outside of the outer periphery of the centrally-located insulating insert 80*.

In all locations radially outside of the outer periphery of the insulating insert 80' there is a magnetic force acting on the arc in'a radially-outward direction. This radially-outward force results from the loop-shaped configuration of the net current path L leading through the electrode to the arc terminal. As is known, the magnetic effect of current following a path of this configuration is to drive the arc in a direction to lengthen the loop, which, in this case, is radially-outward. This radially-outward force varies as a direct function of the current squared.

A factor responsible for the radially-outwardly bowing loop-shape of the net current path L is that the net current enters the base portion 77 from rod 79 at a point disposed radially inwardly of the outer periphery of the insulating insert 80, as will be apparent from FIG. 3.

The radially-outward magnetic force is opposed by an aerodynamic force that tends to drive the arc terminal in a direction toward the center of the stagnation zone. Generally speaking, this aerodynamic force is lowest in the center of the stagnation zone and increases as the boundary of the stagnation zone at S is approached. The magnetic force required to drive an arc terminal radially outward varies approximately in accordance with the curve of FIG. 4, where the minimum magnetic force needed to overcome the aerodynamic force is plotted for difierent positions of the upstream arc terminal as determined by their distance from the center of the stagnation zone.

It will be observed from this curve that when the arc terminal reaches a certain critical distance D from the center of the stagnation region, further increases in magnetic force will be essentially inelfective to drive the arc terminal further radially outward. This distance D is depicted in FIG. 3. The points S of FIG. 2 are at approximately this same distance D from the center of the stagnation zone. When the arc reaches this distance D from the center of the stagnation zone, the air blast is forcing the portion of the arc column adjacent the electrode to generally parallel the external surface of the electrode. Any tendency of the arc terminal to move further upstream (and thus increase the length of the arc column) is blocked by the tendency of the conductive electrode 70 to short out this potential addition to the length of the arc column, inasmuch as this addition would have to extend parallel to and closely adjacent the conductive electrode surface.

The upstream electrode 70 of FIGS. 2 and 3 is so shaped that for all instantaneous currents above around 3,000 amperes and an are present between electrodes 45 and 70, there is a high enough magnetic force acting radially outward on the arc to hold its upstream terminal at the critical distance D from the center of the stagnation zone. This relationship, I have found, produces substantial increases in the rate at which dielectric strength can be recovered when arcing ceases at the current zero, thus improving the chances for successful interruption at this point.

I attribute this increased rate of dielectric recovery to the fact that the upstream arc terminal, when positioned a distance D from the center of the stagnation region is much more directly exposed to the main gas blast than it would be had it been permitted to hang at or near the center of the stagnation zone. This more direct exposure to the gas blast results in more eflicient cooling and scavenging in the crucial arc terminal region due to the higher velocity of the main air blast as compared to the velocity of the eddies in the stagnation zone.

The central insert 80 serves to prevent the upstream arc terminal from entering a region Where there would be no substantial magnetic force on it. In this respect, if the arc terminal were permitted to enter the central region, there would be no appreciable net component of current flowing through the electrode in a radial direction to the arc terminal and thus no significant loop circuit corresponding to L to provide a radially outward magnetic force on the arc. The presence of insert 80 assures that the arc terminal will not enter the central region of low magnetic force.

Another way of precluding entry of the arc terminal into the central region of low magnetic force is to provide a passageway through the electrode that terminates in the central region. Such a construction is shown in FIG. 5 where the passageway is designated 90. A minor blast of air flows through this passageway in the direction of arrow 91 to prevent the are from finding a stable footing in the central region. This electrode of FIG. 5 is otherwise of the same shape as that of FIGS. 1-3 and thus there is a high enough radially outward magnetic force present for currents above 3,000 amperes to hold the arc in the critical position at D referred to hereinabove.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, intend in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

An electric circuit breaker of the type comprising:

(a) a pair of electrodes between which an arc is established during circuit interruption,

(b) an orifice having an opening through which said are is adapted to extend when present between said electrodes,

(c) means for causing a stream of gas to pass through said orifice opening axially of the are about the periphery of said arc,

((1) portions of said gas stream flowing closely adjacent to the electrode located upstream from said are but separating from the surface of said electrode in a region facing the orifice opening, whereby to define a stagnation zone in said latter region,

(e) said arc having an upstream terminal that is held captive in said stagnation "zone during a circuit interrupting operation,

(f) means for preventing entry of said upstream arc terminal into a predetermined central region on said upstream electrode disposed centrally within said stagnation zone,

(g) means for forcing the net current flowing through said upstream electrode to the upstream terminal of an arc located at any point within said stagnation zone outside said predetermined central region to follow a path which extends radially outward to said upstream terminal through the electrode region immediately adjacent said arc terminal, whereby current flowing through said path develops a magnetic force acting radially outwardly on said upstream arc terminal that is a direct function of the current magnitude,

(g') the radially-outward extending portion of said path being located in a region of said upstream electrode sufliciently close to said arc terminal to provide a radially-outward acting magnetic force on said are terminal whenever said arc terminal is located in said stagnation zone outside said predetermined central region,

(h) said upstream electrode being so shaped that the radially-outward acting force present when the arc extends between said electrodes and when the current reaches any value exceeding 3,000 amperes is great enough to force said upstream terminal into a position wherein further increases in said radially-outward magnetic force are substantially inefiective to drive said upstream terminal further away from the center of said stagnation zone,

(i) said upstream electrode being a cup-shaped member having a base portion and an annular flange projecting away from said base portion, said base portion having a surface facing the downstream electrode axial-blast, gas-blast a 7. v to which said upstream arc terminal attaches, said annular flange projecting away from said base portion generally opposite to the direction followed by said gas stream, I

(j) current-directing means for forcing the net current flowing through said upstream electrode to an arc terminal thereon to enter said upstream electrode through said base portion at a location disposed radially inwardly "of the outer periphery of said predetermined central region,

(k) said current-directing means comprising a conductive rod joined to said base portion and surrounded by and spaced radially inwardly from said flange, and

(1) said conductive rod being joined to said base portion in a region generally aligned with said predetermined central region.

References Cited UNITED STATES PATENTS ROBERT K. SCHAEFER, Primary Examiner. R. S. MACON, K. H. CLAFFY, 1. E. CRAWFORD,

Assistant Examiners, 

